To shake the drops off after urinating in one single shake.
Only real men can do this, although two shakes is acceptably manly in private. Three or more and you're masturbating, which is not a manly thing to be doing in private OR public.

Johnboy Walton:

Don't cry BillyJimBob, I know you loved Ellie May, but I could tell from MattBob's Manshake that he deserved her better. One shake was all it took, and I was watchin' his pants for a wet stain all mornin'.